LCD panels made of Low Temperature Poly-silicon (LTPS) may reduce the power consumption of display panels. LTPS TFTs has been widely used because of the advantages of high resolution, fast response time, high brightness, high aperture ratio and the like.
When fabricating a LTPS TFT array substrate, active layer ion implantation is a crucial step for improving the TFT characteristics. FIG. 1 schematically illustrates a cross section of a currently widely-used LTPS TFT display panel. In a conventional process for fabricating LTPS TFT array substrate, a buffer layer P12 is first deposited on a glass substrate P11, then an amorphous silicon (a-Si) is deposited on the whole surface of the buffer layer P12, and the a-Si layer forms poly-silicon layer through a dehydrogenation process and a low temperature crystallization process. After crystallization, the active layer P13 is formed by the pattern process with a mask, which comprises exposing, developing, etching and peeling. And then the ion is implanted into the active layer P13.
In conventional technologies, when ion implantation is performed on the active layer P13, a gate insulating layer P14 deposited on the surface of the active layer P13 is used to protect the surface of the active layer P14 from damage by impact during the ion implantation. Implanted ions enter the active layer P13 through the gate insulating layer P14 and a final ion implantation effect as shown in FIG. 2 is achieved.
However, the characteristics of the gate insulating layer may be degraded because the doped ions may damage the film structure of the gate insulating layer during implanting process as well as some ions may be residual in the gate insulating layer. Furthermore, the ions in the gate insulating layer may be further diffused in later high temperature processes for the LTPS, which will further degrade the characteristics of the gate insulating layer.